The biochemical and morphologic properties of pulmonary vascular endothelial cells are being investigated, using cultures of human pulmonary cells. Specifically, the interaction of the cultured cells with vasoactive peptides is investigated, with respect to the enzymes in cells that degrade or activate peptides. The influence of peptides on specific cell functions is determined. The effects on cell replication, c-AMP, enzyme activities and prostaglandin release are being measured. Of particular interest in this project is the comparison of the properties of pulmonary vascular endothelial cells with other endothelial cells, e.g., from other vascular beds. The cultured cells are used as a model system in which to study the properties of endothelium. Enzymatic activities (angiotensin I converting enzyme, angiotensinase, renin, and other proteases) are measured in cultured cells. Cells from arteries and veins are compared, as are cells from adult and fetal human tissues. Structural correlates for functional properties are sought with the aid of scanning and transmission electron microscopy and the application of fluorescent antibody techniques.